Selective call radio communication systems typically comprise a radio frequency transmitter/encoder (base station) that is accessed via a link to the Public Switched Telephone Network (PSTN) and a radio receiver (e.g., a selective call receiver or the like) that has at least one unique call address associated therewith. Operationally, the selective call receiver receives and decodes information transmitted from the base station, the information having an address and possibly a data or voice message. When the selective call receiver detects its address, it typically alerts the user and presents any received information.
Contemporary selective call radio communication systems such as paging systems employ messaging schemes that can deliver a voice, numeric, or alphanumeric messages to a user. The majority of paging systems transmit address and message information using a protocol such as the GSC (Golay Sequential Code) or POCSAG (Post Office Code Standardization Advisory Group) code. These protocol formats are well known to one of ordinary skill in the art of selective call communication systems. To originate a message or page, the base station or a system controller is typically accessed via the PSTN from a rotary or dual-tone-multi-frequency (DTMF) telephone. As a voice message entry device, the telephone is acceptable, but when graphical information or data needs to be entered, an alternative means of entry is required. Alternative entry devices such as computer terminals and custom entry devices work well when the originators can convey their information to the user in a concise, alphanumeric character based format. However, customer acceptance of these alternative entry devices has been lacking for reasons of expense and operational complexity, particularly in generating and encoding graphics. Facsimile machines are more universally accepted by originators because of their simplicity of operation and their ability to accept almost any paper document, including documents having graphic images.
Selective call receiving devices such as pagers, personal digital assistants, and mobile data terminals are available which receive and display text messages, and some of these devices also can receive facsimile messages and display graphical images. Display screens on such devices, particularly portable devices, are typically physically small in comparison to a normal sheet of paper (e.g., 8.5 inches by 11 inches in the United States). Furthermore, the display screens of some devices are designed having lower image resolution than that used in office facsimile machines. A combination of smaller screen size and lower image resolution results in a reduction of the amount of electronics needed for row and column driving of such displays, the amount of memory needed for storing an image, and the size of a code book required to decode a received message, achieving a smaller and less expensive device, and in the case of portable devices, a device which has longer battery life. The size of the code book is smaller because the size is directly related to the image resolution for which the code book is designed. This works well for messages directed to such devices because not nearly as much information is needed by the users of such devices for a large majority of received messages.
Circumstances arise, however, in which it is desirable to encode, for transmission to a receiver, a target image which has a higher resolution than that for which the code book in the receiver was designed. Thus, what is needed is a means and a method for encoding and decoding a facsimile message having a high resolution using a code book developed for images having a lower resolution.